tldr:
* I installed console-only Debian on an old laptop (no desktop OS at all)
* I added some packages to make it work better for writing:
* network-manager for connecting to hotspots while I'm away
* kmscon for custom fonts and more than 16 colors in the tty
* tmux for a nice status
Apparently there are escape sequences for it; see my response to the parent post.
Even if there weren’t, if a given terminal supported either the older Sixel or the newer KiTTY graphics protocol, it can outright display arbitrary images.
Mainline tmux doesn’t support either protocol, though there’s a fork that does do Sixel. They’re using tmux, so I assume that that’s not the route used.